The present invention relates to electron beam guides such as those used in image display devices and more particularly to a method for compensating for electron beam oscillations within such guides.
Recently, flat image display devices have been suggested utilizing a plurality of electron beam guides to direct electron beams to various positions on a cathodoluminescent screen. One type of these devices is described in copending Patent Application Ser. No. 671,358, now U.S. Pat. No. 4,088,920, filed on Mar. 29, 1976 by W. W. Siekanowicz et al. entitled "Flat Display Device With Beam Guide." The electron beam guide in these devices comprises several apertured plates which are biased so as to establish an electrical field balance between two of the adjacent parallel plates. At the midpoint between the two adjacent plates, the electrical fields are symmetrical looking toward each of the plates. If an electron beam is injected between the two adjacent plates, the balance of electrical field confines the electron beam and guides it in a path parallel to each of the plates. However, if the beam is injected slightly off axis so that its path is not coplanar with the geometrical center between the two adjacent plates, the beam will oscillate above and below the geometrical center. Due to these oscillations, the extraction angle of the electron beam will vary at points where the beam is extracted from the guide and directed toward the screen. This variation in extraction angle at the extraction points produces a shift in the landing position of the electron beam on the cathodoluminescent screen. The deviation in landing position varies in magnitude as the beam is scanned across the screen, depending upon the phase angle of the electron beam oscillations at the various extraction points. Such deviations from nominal landing position, produce brightness variations of light emitted from the phosphor stripes or dots on the cathodoluminescent screen. It is highly desirable in such display devices that the brightness of the cathodoluminescent screen be as uniform as possible over the entire viewing area.